1. Field of the Invention
The present invention relates to the field of power supply devices for light emitting diode (LED) lamps, and more particularly to a linear dimming LED driver circuit capable of adjusting color temperature that provides a higher energy conversion efficiency of the circuit and a better dimming range of the lamps through a single-stage modulation mode of a mono sinusoidal voltage section.
2. Description of the Related Art
At present, most driving devices for LED lamps use a switching power converter as the main circuit architecture, and the switching power converter is a general Fly-back, Forward, Boost, Buck, Push-pull, Half-bridge or Full-bridge circuit. With reference to FIG. 1 for a driving device 1 that uses the boost power converter as the main circuit architecture and has the function of increasing a voltage level required by a load, and the driving device 1 includes a dimming module 10, a rectification module 11, a control module 12 and an output module 13, and the control module 12 includes a control chip 120, a protective resistor 121, the transistor 122 and the sensing resistor 123. The dimming module 10 is a tri-electrode AC switch (TRIAC), and the sensing resistor 123 is connected in series through the transistor 121, so that when the TRIAC switches the conduction angle of an input voltage to adjust the brightness, the sensing resistor 123 detects the driving current of the LED to form a buck to be provided for the control chip 120 to compare the hock with the input voltage to output a high-level voltage or a low-level voltage to the transistor 122, so as to timely conduct or disconnect the transistor 122 to adjust the duty cycle of a Pulse Width Modulation (PWM) signal, and achieve the effect of controlling the outputted driving voltage to change the brightness of the light emitted from the LED. In this method, the driving voltage is increased or decreased in stages according to a change of sine wave of the input voltage. In other words, an output status of a multi-stage modulation is achieved to provide excellent working efficiency of the whole driver circuit. In other words, the working quality can meet the industrial requirements, but a specific component cost is incurred and cannot be lowered further.
In addition, although the conventional lamps adopt a mixture of blue-light LEDs together with yellow-light LEDs to produce a lamp with the required light color, but at the research and design stages of the blue-light LEDs and yellow-light LEDs, the lamps so produced have the issue of a light color error due to the physical properties of different LEDs and cannot be overcome easily. In other words, the number of blue-light LEDs or yellow-light LEDs for actual light emission cannot be increased, so that manufacturers have to inspect and eliminate a large quantity of products with the aforementioned color issue before the products exit the factory. As a consequence, the yield rate is lowered and the inventory of defects is increased, and such consequence is not conducive to the economic development of the industry.
In view of the aforementioned problems, it is a main subject of the present invention to mix the blue-light LEDs with the yellow-light LEDs in the lamp and use them as the light source, and further simplify the circuit architecture and lower the production cost while keeping a high working efficiency and providing a wide dimming range, so as to achieve the effects of flexibly adjusting the light color and improving the cost-effectiveness.